1. Field of the Invention
The present invention relates to a polyamide composition. More particularly, it relates to a polyamide composition having improved impact strength and fabricatability which comprises a polyamide and a modified polyolefin or olefin type elastomer (which can include a nonmodified polyolefin) if necessary with a filler.
2. Description of the Prior Arts
In usual, polyamides have excellent mechanical characteristics, heat resistance, abrasion resistance and appearance. Moreover, the polyamide compositions incorporating an inorganic filler or an organic additive such as a flame retardant have further improved heat resistance, mechanical characteristics, flame retardancy and electric characteristics. Therefore, polyamides and polyamide compositions containing a filler have been used in various fields such as engineering plastics for electric parts, mechanical parts, automobile parts; and extrusion-molding for preparing various molded goods, fibers, films and sheets. The disadvantage of the polyamide molded products have, however, a low impact strength. The polyamides have also disadvantages of inferior fabricatability especially inferior releasing property to easily cause "depression" or "flowmark" and a dimensional instability cause by water absorption, and the polyamide compositions containing an inorganic filler have inferior appearance and "curve" caused by anisotropic shrinkage in comparison with the ABS resins.
The polyamides have inferior impact strength especially in the absolute dried condition just after the melt-molding and accordingly, the polyamides have been used after absorbing water. It has been required to improve the impact strength of the polyamides for improving the molding process. Moreover, a further improved impact strength of the polyamides has been required for using the polyamide in the field of construction substrates beside the fields of functional parts.
The fact of the inferior impact strength of the polyamide molded product means an inferior resistance to cracking propagation of the molded product. This property causes notched brittleness especially brittle break at low temperature. The impact strength can be measured by ASTM D-256 the notched Izod impact strength test or "the weigh falling impact strength".
In order to improve such disadvantages of the polyamide it has been proposed to incorporate various additives in the polyamide, for example, (1) the method of improving the impact strength by melt-blending at least 50 wt.% of a polyamide to an olefin copolymer having an acid component having .alpha.,.beta.-ethylenic unsaturated carboxylic acid group (Belg. Pat. No. 641,952); (2) the method of improving a toughness of weld-line of a polyamide by incorporating an olefin copolymer having .alpha.,.beta.-ethylenically unsaturated carboxylic acid component (more than 10% is neutralized with a metal ion) i.e. ionomer resin in at least 60 wt.% of a polyamide (U.S. Pat. No. 3,845,163); (3) the method of improving an impact strength and a fabricatability of a polyamide composition by incorporating a copolymer made of an alkyl ethylenically unsaturated carboxylate, an unsaturated carboxylic acid and a metal salt of unsaturated carboxylic acid in at least 50 wt.% of a polyamide (Japanese Examined Patent Publication No. 4743/1979) and the method of improving an impact strength by modifying an elastomer with epoxy group and oxy functional group and chemically bonding the product to a polyamide (Japanese Unexamined Patent Publication No. 6693/1975).
The compositions disclosed in the prior arts of the above-mentioned Belgian Patent, U.S. Patent and Japanese Patent Publications are not satisfactory in view of the improvement of impact strength of molded products made of a polyamide composition. Moreover, the compositions have inferior mechanical characteristics and heat resistance to those of the polyamide itself. Therefore, the applications of polyamide compositions in the field of engineering plastics are quite limited. For example, the polyamide composition as the ionomer resin is easily colored into yellow color by an effect of heat or oxygen in comparison with a polyamide itself.